The present invention relates to circuits for generating a control signal to control the carrying out of operations in particular data transfer operations, in a data processing system.
In such systems, to allow data to be transferred between units or subassemblies (to control writing in a memory unit-to give a nonlimiting example) it is often useful to be able to generate a control signal for carrying out an operation when a first voltage with two levels changes from a given one of its levels to the other, only if a second voltage, also with two levels, has already changed from a given one of its levels to the other, and vice versa. One of these voltages may be periodic and the other non-periodic, or alternatively both the voltages may be non-periodic.
The object of the invention is to provide a control signal generating circuit which is capable of activating its output in one of two modes depending on whether a transition occurs between the levels of one of the two voltages before or after a similar transition between levels occurs in the other voltage.